Health Level Seven (HL7) is a standards-producing body, which develops data standards for storing and exchanging information across the healthcare industry. HL7's mission statement is “To provide a comprehensive framework and related standards for the exchange, integration, sharing, and retrieval of electronic health information that supports clinical practice and the management, delivery and evaluation of health services. Specifically, to create flexible, cost effective standards, guidelines, and methodologies to enable healthcare information system interoperability and sharing of electronic health records.”
The HL7 standards cover both clinical and administrative aspects of the healthcare industry, including laboratory, clinical genomics, medical records, patient care, pharmacy, public health reporting, regulated studies, accounts and billing, claims and reimbursement, patient administration and personnel management scheduling.
From 1990 until 2003, HL7 produced a family of message specifications denoted HL7 Version 2. The latest specification in the family is HL7 V2.5, which is incorporated herein by reference. Further information regarding HL7 standards is available at www.h17.org/library/standards_non1.htm.
HL7 V2 messages contain information regarding healthcare-related events such as doctor visits, laboratory test results, and patient observations. The following is a sample V2 message reporting laboratory test results:
MSH|{circumflex over ( )}~\&|||||19941122100053||ORU{circumflex over ( )}M01|EVN|M01|199411181141|PID|||661041||GARDNER{circumflex over ( )}REED{circumflex over ( )}M|PV1||I|E7{circumflex over ( )}703{circumflex over ( )}{circumflex over ( )}LDS|OBR||{circumflex over ( )}A000520|LYTES{circumflex over ( )}Serum Electrolytes|OBX|1|NM|NAS{circumflex over ( )}Serum Sodium|1|138|mmol/L|OBX|2|NM|K{circumflex over ( )}Serum Potassium|1|3.2|mmol/L|OBX|3|NM|CL{circumflex over ( )}Serum Chloride|1|114|mmol/L|OBX|4|NM|CO2{circumflex over ( )}Serum CO2|1|24|mmol/L|
Each V2 message consists of segments, represented by rows in the example shown above. Each segment begins with a three-letter code defining the segment type. The first segment is the message header, denoted MSH. The PID (“patient Identifier”) segment contains patient identification information. Other segment types include PV1, which stands for “patient visit,” and OBX, which stands for “observation.” A table listing additional segment types is given in the detailed description section hereinbelow.
HL7 V2 segments are divided into data fields, separated by vertical bar symbols, each field containing data elements. Data elements may conform to any of several data types including text characters, such as a patient name, or numerical information, such as a patient age or a quantitative blood test result. Complex data types, including two or more data elements, are also defined. Data fields may be defined as “required” or “optional,” and may be repeated several times within a segment.
During the late 1990's, work began on a new family of message specifications, later to be published as the HL7 V3 specification. HL7 V3 follows an XML structure. For a better understanding of the methods to be described, the concept of XML-based structures will now be explained in greater detail.
XML (Extensible Markup Language) is a simplified version of Standard Generalized Mark-Up Language (SGML), designed initially for Web documents. XML allows designers to create their own customized markup languages, enabling the definition, transmission, validation, and interpretation of data between applications and between organizations. XML is a formal recommendation of the World Wide Web Consortium (W3C). Additional information regarding XML is available at www.w3c.org/xml. Markup symbols are used in XML to describe the contents of a page or file, defining the meaning of the data that is being described. The term “markup” refers to a sequence of characters or other symbols that are inserted at certain places in a document, to describe the document's storage layout and logical structure. The markup symbols are often called “tags.” XML is extensible due to the fact that the markup tags are user-defined, thereby enabling the designer to define a complete language to suit a particular application. The designer defines a DTD, or Document Type Definition, which is a collection of XML markup declarations that, as a collection, defines the structure, elements, and attributes that are available for use in a document that complies with the DTD. The designer may also use the newer XSD, or XML Schema Definition format for defining tags.
The HL7 V3 family of specifications is centered around a single, unified Reference Information Model (RIM) covering all domains of the healthcare industry. The RIM defines all data structures, data types and vocabularies, as well as the relationships between them. The RIM includes dozens of classes, representing the building blocks from which all healthcare-related messages and documents are built.
Four fundamental classes are defined: Entity, Role, Participation and Act. Other classes are typically specializations of one of the fundamental classes. For example, a Procedure class representing a medical procedure is a specialization of the Act class. Observations are specializations of Acts as well, representing laboratory orders and results, diagnoses and more. Patients and healthcare providers are represented through the associations of Entity-Role-Participation.
For example, a person is an Entity that may have the Role of a physician and the Participation of an attending physician in the Act of admitting a patient to a hospital. Each class contains attributes that carry information about the class. Each attribute is formatted according to a predefined data type. The class attributes and data types are defined in the RIM. Using this class representation, any healthcare-related event can be expressed in terms of a unified, predefined data structure. Further details regarding HL7 V3 can be found at www.hl7.org/library/standards_non1.htm.
All HL7 V3 specifications are reductions or specializations of the RIM to address the needs of specific usages in the healthcare industry. For example, the Clinical Document Architecture (CDA) is a specification for producing and exchanging clinical documents, derived from the HL7 RIM, in a standard, XML-based structure. Further details of the CDA specifications can be found in a publication by Dolin, et al. entitled “HL7 Clinical Document Architecture, Release 2, Committee Ballot #02,” Dec. 8, 2003, published by the HL7 Structured Documents Technical Committee, which is incorporated herein by reference. The CDA specification documentation is also available from www.hl7.org/Library/Committees/structure/CDA.ReleaseTwo.CommitteeBallot02.Dec.2003.zip.
A derivation of the RIM for a particular usage is sometimes referred to as a “schema” or “XML schema.” Other XML schemata derived from the RIM cover Regulated Clinical Research Information Management (RCRIM), Clinical-Genomics, Medication, etc.
In addition to HL7 V2 and V3, a version denoted HL7 V2.XML was approved by the HL7 organization, consisting of encoding rules for converting HL7 V2 messages into XML format. Further details regarding HL7 V2.XML are available in an HL7 Specification entitled “HL7 Version 2: XML Encoding Syntax, Release 1,” Jun. 4, 2003, which is incorporated herein by reference. Several commercial conversion tools have been developed for converting HL7 V2 messages to HL7 V2.XML format. Such tools are available, for example, from iNTERFACEWARE Inc. of Toronto, Canada (www.interfaceware.com), or from Lumrix.net of Bern, Switzerland (www.1umrix.net/hl7xml.php).